576 research outputs found
Feasibility of study magnetic proximity effects in bilayer "superconductor/ferromagnet" using waveguide-enhanced Polarized Neutron Reflectometry
A resonant enhancement of the neutron standing waves is proposed to use in
order to increase the magnetic neutron scattering from a
"superconductor/ferromagnet"(S/F) bilayer. The model calculations show that
usage of this effect allows to increase the magnetic scattering intensity by
factor of hundreds. Aspects related to the growth procedure (order of
deposition, roughness of the layers etc) as well as experimental conditions
(resolution, polarization of the neutron beam, background etc) are also
discussed.
Collected experimental data for the S/F heterostructure
Cu(32nm)/V(40nm)/Fe(1nm)/MgO confirmed the presence of a resonant 60-fold
amplification of the magnetic scattering.Comment: The manuscript of the article submitted to Crysstalography Reports.
23 pages, 5 figure
A hydrodynamic model for asymmetric explosions of rapidly rotating collapsing supernovae with a toroidal atmosphere
We numerically solved the two-dimensional axisymmetric hydrodynamic problem
of the explosion of a low-mass neutron star in a circular orbit. In the initial
conditions, we assumed a nonuniform density distribution in the space
surrounding the collapsed iron core in the form of a stationary toroidal
atmosphere that was previously predicted analytically and computed numerically.
The configuration of the exploded neutron star itself was modeled by a
torus with a circular cross section whose central line almost coincided with
its circular orbit. Using an equation of state for the stellar matter and the
toroidal atmosphere in which the nuclear statistical equilibrium conditions
were satisfied, we performed a series of numerical calculations that showed the
propagation of a strong divergent shock wave with a total energy of 0.2x10^51
erg at initial explosion energy release of 1.0x10^51 erg. In our calculations,
we rigorously took into account the gravitational interaction, including the
attraction from a higher-mass (1.9M_solar) neutron star located at the
coordinate origin, in accordance with the rotational explosion mechanism for
collapsing supernovae.W e compared in detail our results with previous similar
results of asymmetric supernova explosion simulations and concluded that we
found a lower limit for the total explosion energy.Comment: 13 pages, 5 figures, 2 table
Pion and muon production in electron-positron photon plasma
We study production and equilibration of pions and muons in relativistic
electron-positron-photon plasma at a temperature . We argue
that the observation of pions and muons can be a diagnostic tool in the study
of the initial properties of such a plasma formed by means of strong laser
fields. Conversely, properties of muons and pions in thermal environment become
accessible to precise experimental study.Comment: 16 pages, v3 imporved presentation in response to PRD review, v4
minor corrections presumably the "to be" published versio
Direct evidence of soft mode behavior near the Burns' temperature in PbMgNbO (PMN) relaxor ferroectric
Inelastic neutron scattering measurements of the relaxor ferroelectric
PbMgNbO (PMN) in the temperature range
490~KT880~K directly observe the soft mode (SM) associated with the
Curie-Weiss behavior of the dielectric constant (T). The results
are treated within the framework of the coupled SM and transverse optic (TO1)
mode and the temperature dependence of the SM frequency at q=0.075 a* is
determined. The parameters of the SM are consistent with the earlier estimates
and the frequency exhibits a minimum near the Burns temperature (
650K)Comment: 6 figure
A Rotating Collapsar and Possible Interpretation of the LSD Neutrino Signal from SN 1987A
We consider an improved rotational mechanism of the explosion of a collapsing
supernova. We show that this mechanism leads to two-stage collapse with a phase
difference of \sim 5 h. Based on this model, we attempt a new interpretation of
the events in underground neutrino detectors on February 23, 1987, related to
the supernova SN 1987A.Comment: 18 pages, 3 figures, 9 table
Formation of droplets of the order parameter and superconductivity in inhomogeneous Fermi-Bose mixtures (Brief review)
The studies of a number of systems treated in terms of an inhomogeneous
(spatially separated) Fermi-Bose mixture with superconducting clusters or
droplets of the order parameter in a host medium with unpaired normal states
are reviewed. A spatially separated Fermi-Bose mixture is relevant to
superconducting BaKBiO3 bismuth oxides. Droplets of the order parameter can
occur in thin films of a dirty metal, described in the framework of the
strongly attractive two-dimensional Hubbard model at a low electron density
with a clearly pronounced diagonal disorder. The Bose-Einstein condensate
droplets are formed in mixtures and dipole gases with an imbalance in the
densities of the Fermi and Bose components. The Bose-Einstein condensate
clusters also arise at the center or at the periphery of a magnetic trap
involving spin-polarized Fermi gases. Exciton and plasmon collapsing droplets
can emerge in the presence of the exciton-exciton or plasmon-plasmon
interaction. The plasmon contribution to the charge screening in MgB2 leads to
the formation of spatially modulated inhomogeneous structures. In metallic
hydrogen and metal hydrides, droplets can be formed in shock-wave experiments
at the boundary of the first-order phase transition between the metallic and
molecular phases. In a spatially separated Fermi-Bose mixture arising in an
Aharonov-Bohm interference ring with a superconducting bridge in a
topologically nontrivial state, additional Fano resonances may appear and
collapse due to the presence of edge Majorana modes in the system.Comment: 18 pages, 10 figures, submitted to JETP Let
Peierls Instabilities in Quasi-One-Dimensional Quantum Double-Well Chains
Peierls-type instabilities in quarter-filled () and half-filled
() quantum double-well hydrogen-bonded chain are investigated
analytically in the framework of two-stage orientational-tunnelling model with
additional inclusion of the interactions of protons with two different optical
phonon branches. It is shown that when the energy of proton-phonon coupling
becomes large, the system undergoes a transition to a various types of
insulator states. The influence of two different transport amplitudes on ground
states properties is studied. The results are compared with the pressure effect
experimental investigations in superprotonic systems and hydrogen halides at
low temperatures.Comment: 7 pages, RevTeX, 9 eps figure
Magnetic and Superconducting Phase Diagram of Nb/Gd/Nb trilayers
We report on a study of the structural, magnetic and superconducting
properties of Nb(25nm)/Gd()/Nb(25nm) hybrid structures of a
superconductor/ ferromagnet (S/F) type. The structural characterization of the
samples, including careful determination of the layer thickness, was performed
using neutron and X-ray scattering with the aid of depth sensitive
mass-spectrometry. The magnetization of the samples was determined by SQUID
magnetometry and polarized neutron reflectometry and the presence of magnetic
ordering for all samples down to the thinnest Gd(0.8nm) layer was shown. The
analysis of the neutron spin asymmetry allowed us to prove the absence of
magnetically dead layers in junctions with Gd interlayer thickness larger than
one monolayer. The measured dependence of the superconducting transition
temperature has a damped oscillatory behavior with well defined
positions of the minimum at =3nm and the following maximum at =4nm;
the behavior, which is in qualitative agreement with the prior work (J.S. Jiang
et al, PRB 54, 6119). The analysis of the dependence based on Usadel
equations showed that the observed minimum at =3nm can be described by the
so called "" to "" phase transition of highly transparent S/F
interfaces with the superconducting correlation length nm in
Gd. This penetration length is several times higher than for strong
ferromagnets like Fe, Co or Ni, simplifying thus preparation of S/F structures
with which are of topical interest in superconducting
spintronics
Surface structure of Quark stars with magnetic fields
We investigate the impact of magnetic fields on the electron distribution in
the electrosphere of quark stars. For moderately strong magnetic fields G, quantization effects are generally weak due to the large number
density of electrons at surface, but can nevertheless affect the spectral
features of quark stars. We outline the main observational characteristics of
quark stars as determined by their surface emission, and briefly discuss their
formation in explosive events termed Quark-Novae, which may be connected to the
-process.Comment: 9 pages, 3 figures. Contribution to the proceedings of the IXth
Workshop on High Energy Physics Phenomenology (WHEPP-9), Bhubaneswar, India,
3-14 Jan. 200
Conservation laws of semidiscrete canonical Hamiltonian equations
There are many evolution partial differential equations which can be cast
into Hamiltonian form. Conservation laws of these equations are related to
one-parameter Hamiltonian symmetries admitted by the PDEs. The same result
holds for semidiscrete Hamiltonian equations. In this paper we consider
semidiscrete canonical Hamiltonian equations. Using symmetries, we find
conservation laws for the semidiscretized nonlinear wave equation and
Schrodinger equation.Comment: 19 pages, 2 table
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